Method and apparatus for producing helical gears



war- I D Aug. 4, 1959 E. WILDHABER 2,897,634

METHOD AND APPARATUS FOR PRODUCING 'HELICAL GEARS Filed Nov. 27, 1953 eSheets-Sheet 1 I l l i I INVENTOR. 43 E- WI LDHABER FIG. 6

A t'l'ame 1959 WILDHABQER 2,897,634

METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS Filed Nov. 27, 1953 6Sheets-Sheet 2 IN VEN TOR.

BY q

Afforrmf f E- WILDHABERV 4, 1959 E. WILDHABER 2,397,634

METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS Filed NOV. 27, 1953 6Sheets-Sheet 3 6 so '3 I00 I I2 35 I22" I s? I97 |2o' IN V EN TOR:

E- WILDHABER Aug. 4, 1959 E. WILDHABER 2,897,634

METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS Filed Nov. 27, 1953 Y 6Sheets-Sheet 4 7T6? i no FIG. 0

INVENTOR: E WILDHABER BY Z Attorn y Z Aug. 4, 1959 E. WILDHABER METHODAND APPARATUS FOR PRODUCING HELICAL GEARS Filed NOV. 27, 1953 6Sheets-Sheet 5 2 r w G H w R E mB l Y F/Q E FIG.27

Aug. 4, 1959 wlLDHABER 2,897,634

METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS Filed Nov. 27, 1953 sSheets-Sheet 6 2| 276 Z, 2?? 23l\. 277 252' 220 4 y -27? KW my 28l 28428 Q) 282 285 METHOD AND APPARATUS FOR PRODUCING HELICAL GEARS ErnestWildhaber, Brighton, N.Y.

Application November 27, 1953, Serial No. 394,645

25 Claims. (Cl. 51-52) The present invention relates to the productionof helical teeth and more particularly to the production of helicalteeth on gears which are to run either on parallel or non-parallel axes,and to the production of helical threads on worms and screws, especiallyhelical threads of substantial lead angle. In a more specific aspect,the invention relates to the production of helical teeth and threadswith rotary tools having formed cutting profiles, either milling cuttersor grinding wheels. Still more specifically, the invention relates tothe production of helical teeth and threads with milling cutters or withgrinding wheels that have concavely curved side profiles and whichproduce convex tooth profiles on the work.

Because a grind wheel is a cutter with an infinite number of cuttingedges, and because the invention is especially useful in grinding, weshall describe it hereafter in reference to its particular applicationof grinding helical gear teeth, but it is to be understood that this isintended in no way to limit the scope of he claims.

In a form-grinding operation the profile shape of the grinding wheeldepends on the profile shape of the teeth or threads to be produced, butwith helical teeth or threads the profile shape of the wheel is not adirect counterpart of the profile shape of the teeth or threads to beproduced. This is because the contact between a grinding wheel and thehelical teeth it grinds extends obliquely across the grinding surfaceand is not contained in a plane normal to the teeth and containing theaxis of the grinding wheel. For this reason the wheel profile in thatplane is less curved than the tooth pro file. The wheel profile dependsalso on the diameter of the grinding wheel. The larger the wheeldiameter the larger becomes the curvature radius of the wheel profile ata given mean point. For very large wheels, the wheel profile approachesa straight line, when the wheel is intended to grind involute helicalteeth, which are the usual helical teeth.

The dependence of the wheel profile on the wheel diameter is one of thedifiiculties of grinding helical gears or threads with a formed wheel.Another difliculty lies in dressing the wheel to the desired shape.

These difliculties with grinding helical gears or threads are magnifiedwhere an attempt is made to grind opposite sides of the teethsimultaneously. The customary practice is to adjust the grinding wheelto the helix angle at the pitch circle; but then one side of the wheelis apt to run out of grinding contact before the other, at the ends ofthe tooth spaces. This occurs especially where he teeth have long orlengthened addenda, which is often the case with pinions; and it occurseven with teeth of standard addenda. When grinding continues on one sideand ceases on the other side, the grinding pressure becomes unbalancedso that the grinding wheel tends to spring away from the surface stillbeing ground and to leave more stock on the back end of the tooth. Thislittle extra stock may result in gear noise and reduced gear life.

atg

. of a .tooth .space of the work.

A further object of the invention is to provide a 7 method of cutting orgrinding helical teeth in which both "ice With previous methods ofproducing helical gears and threads, moreover, it has not been practicalto produce the localization of tooth bearing or evase ofi at the ends.of the teeth that is desirable to render the teeth less sensitive todisplacements and deflections under load, and less sensitive tomanufacturing inaccuracies and tolerances. 7

With ease-0E of the tooth surfaces at the tooth ends, the tooth contactdoes not sweep the entire working surface of the teeth in any givenmounting position under a light load, but only a portion thereof. Thetooth bearing is localized and is confined to a restricted area.

The desired form of this bearing area is bounded by something like anellipse or oval, whose major axis extends in the direction of the teeth.No grinding method has heretofore been known which can actually achievethis form of tooth bearing on helical teeth of cylindrical gears. Nor isthere any cutting method known to achieve this shape on helical teethwith a formed disk milling cutter.

One object of the present invention is to provide a process in whichboth sides of a tooth space can be cut or ground simultaneously whilemaintainingthe opposi-te cutting or grinding pressures in balance duringcutting or grinding of the full length of opposite sides sides of atooth space are cut or ground together and in which cutting or grindingcontact ceases nearly simultaneously on the two tooth sides.

Anothere object of the present invention is to provide a method andmeans for producing localized tooth bearing or ease-off on helical gearteeth, and broadly tocontrol the shape of the tooth bearing area. I

Another object of the invention is to provide a method and means forcutting or grinding helical teeth in which localization of tooth bearingor ease-oflf at the tooth ends can be attained and controlled both andas to shape.

Other objects of the invention will be apparent hereinafiter from thespecification and from the recital of the appended claims.

In the drawings: a

Fig. l is a side elevation of ahelical gear, illustratingdiagrammatically the conventional procedure in grinding a helical gearwith a formed wheel, and showing the two zones of grinding engagement ofthe wheel with sides of a tooth space of the gear;

Fig. 2 is a side elevation of a helical gear, but illustrating oneembodiment of the present invention and showing how the two zones ofgrinding engagement of the wheel with opposite sides of thetooth spaceare aligned with each other axially;

Fig. 3 is a fragmentary view taken perpendicular to the axis of the gearand further illustrating the process of the present invent-ion, the gearbeing'slrown in sec tion and the grinding Wheel being shown partly insection Fig. 5 is a side elevation of a helical tooth, and illus tratingthe form of ease-off or localization of tooth bear ing desiredlengthwise of the tooth;

Fig. 6 is a View similar to'Fig. 5 showing the desired shape of thelocalized tooth bearing obtained through,

ease-oiflengthwise and profilewise on a tooth;

Fig. 7 is a fragmentary normal section through the tooth space of ahelical gear, illustrating a somewhat modified procedure;

Figs. 8 to 11 inclusive are diagrammatic views repreas to amountopposite sition nearthe tooth end with one side in grinding con- E s- 11is e ra n a y. ew ta en at rialit' sl s t l qn 9f the te t .shn iu exa ea d y th p tion o v e r n i swh la j ce t hericpt .e d;

ias fii a disa m f r er.ex l n toryn it en Qt. f

obtaining a desired forrn of tooth ease-elf in accordance with thepresent invention;

F s- :14 i a m a y ir i g l i g h h" a grinding Wheel h adb ltt a e tirthenr s ti r tion, the section being taken at right angles to the axisof the grinding wheel; I d I A p FigflS is an axial section through thegrinding wheel andits mounting;

Fig. 16'is a cross section threu uja' modified ltor rn of wheelhead, andtaken "at rightangles to the axis at the grinding wheel; d

Fig. 17 is an axial section of the wheel head shown'in Fig. 16;

Fig. '18 is an end view of the wheel head ofFigs. 16 and 1 7 with thedust seal and dust cover removed therefrom; r,

Fig. 19 is a fragmentarytransversesection through the wheel head ofFigsflfi to 18 and showing particularly a cylindrical slide used indisplacing the wheel transversely of its axis; I d

Fig. 20 is a more or less diagrammatic plan view of one form of grindingmachine constructed in accordance with the present invention;

, Fig. 21 is a drive diagram of the machine shown in 2 V Fig. 22 is aView showing a partial axial section of a grinding wheel, andillustrating the principle of operation of the" wheel dresserconstructed according to the present invention; d I

Fig, 23 is a fragmentary normal section along the line 23-43015 Fig. 22,looking in the direction of the arrows;

Fig. 24 is an axial section of a wheel dressing or truingdevice-constructed in accordance with one embodiment of my invention,the section being along the drawing plane of Fig. 23;

Fig. 25 is an end view taken from the left of Fig. 24 and J showing theadjustable part ofthe dresser which holds the diamond; V i

Fig. 26 is a fragmentary section similar to Fig. 24 illustrating amodified construction;

Fig. 27 .is a development to a plane of a part of the circumference of acam used in dressers constructed 'ac-' cording to my invention, andshowing this cam in contact with an abutment. or follower;

Fig. 28 is a diagrammatic sectional view of a device constructedaccording to the present invention'for dressing or truing opposite sidesof a grinding wheel simultasly;

Fig. 29 is a diagrammatic view, partly in section, of a modified form ofdressing or truing device, for dressing or truing both sides of a reiand. a. r a Fig; 30 is a diagram corresponding to Fig 29 illustratingan operative connection.

grinding wheel of curved axial Referring now to the drawings by numeralsof refer;

encef35 denotes a helical gear; and 36 denotes the axis of this gear. Inconventional practice, the grinding Wheel,"

the two opposite tooth normals which pass through the,

point 38 are what is known as contact normals. They contain the pointsof contact 39 and 40 between the grinding wheel W and the profiles ofthe opposite sides 41 and 42 of the helical teeth 43 of the gear. Thepoints 39 and 40 are low onthe tooth profiles '41 and 42, lower than thepitch point" 38, that is, closer to the tooth bottom. This low positioncauses the two oblique lines 45 and 46 of grinding contact to havedifferent axial positions. Line 45 is closer to the upper end 47 of thegear 35 than the line 46. v a

Ingrinding'a tooth space, the work 35 and the grindingwheel W move inahelical path about the axis 36 relative to eachother' as the wheelrotates on its own axis. Asregards relative positions and grindingcontact, the helical motion can be considered performed entirely. by thework 245. ,Atfonefltime, then, the. gear end 47 will be ina position asshown by dotted lines 47 In thisv end position only a small end portionof the grinding line 45 remains on the work while most of the grindingline 46 is still on the work. It is seen then that grinding contactceases on tooth side 41 long before it ceases on the opposite side 42.In the middle regioniof the teeth, the grinding pressure on one sideprovides some direct bal ance to the grinding pressureon the oppositeside.

tooth space with the end of grinding contact on the opposite side of thetooth space. The wheel tends to spring Inaccordance with one. phase ofthe present'inventionthis deficiency is remedied by setting thefgrindingwheel W (Fi'gs. 2 3 and 4) to a diiferen't angular position and bymodifyingits shape accordingly. The grinding wheel is set toa largerhelix angle than the'helix ,angle-atthe pitch radius of, the gear. ,Inthejembodiment illustrated. in Figsf2and'3 it is so set"thatthegririding'lines45" 46 lpassthrough mean-points 50', 51 of the toothprofiles in a transverse section, that is, in a section perpendicular tothe Work axis as'indicat'ed in Fig;: 3. l In this Way the grinding lines45 46 have substantially equal axial positionslf When the upper end 47bof the pinion is intheposition ,47' (Fig, '2), then, one halflof eachgrinding line 45' "46" remains onthe Work; Contact ceases s'ubstantiallyat thesanieitimeon bothfsides, There is no unbalanced pressure betweenthe two sides.

, Helix angle setting Thedet'ermination of the angular setting of the"grind-J ing wheel will now be described so that the grinding lines Thetooth surface normals 52, saga: points 50,51 arefirst determined. Oninvolute gears they are tangent to the base circles (not shown), as'well'known, and areinclined "to the plane of rotation, that is, to thedrawing plane of Fig.

pass through meanpoints 50, 51.

3, at an angle equal to the known base helix angle. Next their.intersection points 55, 56 with the, plane 57 are determined. This planecontains the wheel axis 60 and is parallel to the axis 36 of the work.

The axis 60 of the grinding wheel W is the straight line connecting theintersection points 55, 56, for the t 7. the tooth ends however, thisbalance is disturbed. The H balanced support for the wheel ceases on oneside of the The crest of this wave projects normals to a, surface ofrevolution all pass through its axis. By fulfilling this condition asdescribed, the normals 52, 53 are made contact normals, namely, normalswhich are common between the work and the grinding wheel.

The working surface the grinding wheel The working surface of the wheelis best determined by first determining the line of contact between theworking surface of the wheel and a helical tooth side of the Work 35.After the line of contact is determined, with all the contact normalsalong it, these contact normals and contact points are turned about theaxis of the grinding wheel into a single axial plane of the grindingWheel. The contact points are then points of the grinding profile inthis position, and the turned contact normals are normals to thegrinding profiles.

As shown in Fig. 2 the contact normals 52, 53 do not intersect. However,there is one pair of contact normals which intersect. They intersect ona radial line 59 at a point 61 (Figs. 3 and 4). This point is located atsuch a radius 3661=r' (Fig. 3) that the helix angle 1/1 at said radiusis equal to the helix angle setting of the grinding wheel determinedabove.

r can be determined from the well known equation for the helix angle1,0:

L. tan ,0

Like all normals of a surface of revolution, the surface normal at eachpoint of the line of contact intersectsthe axis of the grinding wheel orrotary cutter. To determine the contact position at a given radius ofthe helical tooth surface, the surface normal at that radius is moved ina helical path along the tooth surface until it intersects said axis. Inthis imaginary displacement along and about the axis of the helicalsurface, the original normal continues to be a tooth surface normal; andthe point where it intersects the tooth surface in its final position isa point of contact between the tooth surface and the working surface ofthe grinding wheel. Other points, corresponding to different radii aresimilarly determined, to obtain a series of points defining the line ofcontact.

The line of contact can also be considered the normal projection of thewheel axis to the tooth surface. It can be demonstrated mathematicallythat it can also be con sidered the normal projection to the toothsurface of another straight line, which is located nearer the toothsurface and is more convenient for determining the line of contact. Thecontact normals all pass through this other line 62 (Fig. 2). Itconnects points 61 and 63 (Figs. 2 and 3). The latter point isobtainable by spacing a unit distance (1 inch) from point 61 on a linedrawn through this point parallel to the gear axis 36, to point 65 (Fig.2); From point 65 the distance u defined below is measured oif on a line6563 parallel to the wheel axis 60. It is measured on the same scale assaid unit distance.

Herein R denotes the radius of the grinding Wheel to point 61, that is,center distance, G minus r (C -r').

The axial profile of the grinding wheel can bedeter mined from thepoints and normals of the line of contact I along oblique lines, thegrinding wheel profile in the normal section (Fig. 4) is less curvedthan the convex 6. tooth profile. The said normal section isperpendicular to the direction of the teeth and contains the axis of thegrinding wheel. It is also an axial section of the grinding wheel.

.The difference between the profile curvatures of the grinding wheel andthe work in the normal section can best be illustrated by the centersofcurvature of the two profiles. 66, ,66' (Fig. 4) denote the contactnormals which pass through the point 61. The centersof curvature 67,67', 68, 68 of the contacting profiles of this normal section lie onthese normals. The tooth profile curvatures and the location of theircurvatures centers 67, 67' are known. The curvature centers 68, 68' ofthe wheel profiles can be obtained from the wheel profiles as determinedabove. The distances of the curvature centers of the wheel profiles,from the curvature centers 67, 67' of the tooth profiles depend on thewheel radius R to point 61, on the helix angle setting 1/, and oninclination p of normals 66, 66 to a plane 69 perpendicular to radius59. Distance Ap is equal to 67-68 (6768') can be shown to amountapproximately to:

Ap R tan 4/ sin This distance A increases with increasing wheel radius.The larger the wheel, the more its profile approaches the profile of arack which in the involute gear system is straight.

In the drawings, the wheels are shown small enough to keep them withinthe drawing space provided. Larger wheels are preferably used inpractice.

Instead of aligning the axial positions of the grinding lines 45', 46'completely, it is also possible to align them only partially. Thus, themean points of contact 50', 51', may be assumed in a normal plane (Fig.7) rather than in a transverse plane perpendicular to the work axis 7 aswas done in Figs. 2 and 3. V

On the larger member of a gear pair with corrected tooth proportions,that is, with shortened addendum and lengthened dedendum, the twogrinding lines are often sufficiently aligned in the conventionalprocedure so that they do not require my special procedure justdescribed. In general, the special procedure described results in animprovement of the gear pair by improving either one or both members. Itrepresents the preferred procedure and can be practiced without anychange in machine structure.

Another and very important feature of the present invention is theprocedure to attain the desired form of tooth ease-off or localizationof tooth bearing. The

teeth are eased ofi near their boundaries, lengthwise and profilewise,so that they bear over a localized area when run at light load in theirexact position. Slight changes in the mounting, deflection under load,inaccuracies even within tolerances, displace the bearing area on thetooth surface, but with properly eased-off teeth, the teeth will neverhear hard at their ends. Without ease-off this may occur. Tooth ends arethen more apt to break off under fatigue and noise is more apt todevelop. The result is that eased-off teeth are stronger and better.

Referring first to the lengthwise ease-0E only, without profileease-off, a generally square or rectangular hearing area is desired.This is shown at 70 in Fig. 5. It is the area between the straight lines71, 71'. 45" is the line of grinding contact inthe mean position. Dottedlines 45 and 45 are lines of grinding contact on opposite sides of line45" and are generally similar to line 45".

In the known methods of grinding ease-0E the wheel is moved slightlydepthwise adjacent both ends of the teeth. There is no depthwise motionat the middle of the teeth. This procedure is satisfactory on straightteeth; but on helical teeth it produces a form of ease-off differentfrom the one intended. The ease-01f follows 7 the line or grindingcontest; At end profile assess, the e localized tooth bearingfobtaindfinthis known rmethod is an area likethe onbofifided .bylines45 and45 It Qis at a bias. Too much ,stock has been removed at the diagonal corners73, 73',and not enoughat the diagonal 5 commune. v

We can plot, the ease-ofijat the various points of jthejf toothsurface'iby connecting points iof equal e se-on thereby obtaining ageodetic mapofthe'ease ofi surface Line 45", is a line of zero ease-elf.If line's 45 a'ndi4S are"consider'ed lines of constant andequalease-oft, then their inclination'or slant depends to'soniegfexte'fltonthe curvature or the wheel profile. But in "any averaged "slant issubstantially equal to'th'eTsl v 45". Heretofore, there has been no'knewmway of '15 avoiding the bias condition. I p v v The p esentinvention, however, permits "of, attaining a localized bearing'are'a asboundedhy lines 71, 71"when; only-lengthwise ase-offisconsideredjfandjan ovalfareafj 75 such as shown'in Fig. '6 whenfprofileea fij is add Further, any form of bearing area maybe attained, what"ever may be held desirable. *The methodof the present invention providesfull control of thebearing area. It can be kept free of slant asnormally desired,: or it can be slanted one way or the other. 7 Thepresent invention enables full control as to where to pIacYhecas'e Sfi';and how much of it to provide. 7

Principles of controlled tooth 'eizs-ofi The explanatory diagrams' Figs.8 to ll can 3 sidered a partial development to a plane ofi a cylindricalmid-section laid through the gear teeth. The axis open cylindricalsectional surface coincides with the'gear axis; 36. The section may betaken along the pitch c ylinder j' of the gear. In other Words, thefiguresshow developed portions of the peripheral surface of the gear.For clarity, the sections have not been cross-hatched. p

In Fig. 8, 77 denotes the grinding wheel section in the mid-position ofthe grinding wheel. Its axis is parallel to line 78 and above it. If noease-ofi were provided,. the considered cylindrical surface wouldintersectjthe tooth sides in helices. These show up in the develop mentas straight lines 79 in Fig. 8. With ease-o ffl the developedintersection lines with the tooth sides are convex curves 80 tangent tolines 79. Their curvature is very much exaggerated. At the tooth ends,the curves 80 have a normal separation z from their mean tangents 79,,which on gears of the size, of automotiye transmis sion gears, amountsto something in the order Qf 0.00 l

inch. This is at a distance s from thepoint of tangency with a line 79,which distance depends upon the length of face F and on the helix angleof the gear.

"'2 cos g0 At the "small mean: at z considered; instantiated? anddistances are tied up with the radiusR or 'cui'vature radius like theordinates era parabola,naniely,

. ,sL, Z and a This determines radiusR Each are 80 has a varying'inclination to the direction of -its tangent 79. Q It is zero at themiddle 'and' increases toward the ends; At the'tooth ends theinclination t' of a curve 80 to its mean tangent 79 amounts to:

Are tin radians teetert. .s f This can be transformed into:

The wheel position for generating the eased-off tooth end willnowbedeteiniined, first for'grinding a single side. For this referencewill be made to Figs. 9 and 10. The dotted section 77 again representsthe grinding wheel position for grinding truly helical .tooth sides 79without ease-off. At the upper end of the tooth space contact hasshifted in the directionof the gear axis 36 from a mean position" 81 toend point 81. To obtain satisfactory eased-0E teeth We must kee thepressure angle constant along each side'ofa tooth space from end to endof a tooth.

To form the eased-oil tooth ends, the'grindi ng' wheel:

is, as in conventional practice, vfeddepthhris intothe work as ittravels from a central position lengthwise of. the work to either end ofa tooth space. But as indi cated by section 77.,, the wheel shouldcontact curve 80 immediately adjacentpoint 81". Only then will itbepossible to retain the same inclination of the tooth sur face normalto the cylindrical surface as on the true .helicoid. The preservation ofthis inclination or pres tion immediately adjacent point 81 as curve 80.'This object could be attained in dilferent ways if the'wheel weregrinding only one side of a tooth 'space at jatime'. The wheel could forinstance, be slightly turned about any axis passing through 81' andcontained in the normal plane perpendicular to the tooth direction. Noneof these turning adjustments would affect the'pressureangle.

:In other words; an infinitesimal turning adjustment of this kind wouldcause a pressure angle change whichjis infinitesimal in the secondorder, and is entirely negligible.

One position of the turning axis fits both sides of the .tooth spaceequally well and results in simplicity besides'f' This axis is parallelto the axis of the grinding wheel, and may also pass through point 81.

Fig. 9 shows its effect. The tooth surface normal 81"-82 before ease-offis inclined to the drawing plane of Fig. 9 at what'may be called thenormal' pressure angle at 81' so' that the endpoint 82 'is below thedrawl ing plane. The turning axis 85 lies in the drawingplane.

As normal 81'82 is turned about axis' 85 its point 82 describes a circlewhich is projected as a straight line in i 'Fig. 9. Point 82 therebymoves to a position 82' so. 7 that normal '81'82' is perpendicular tocurve 80. In

this new position of the normal its inclination to the drawing plane hasnot changed at all. Through this a turning adjustment the grinding wheelis now capable of contacting curve 80 immediately adjacent pointSl' asrequired. The turning displacement on axis 85 moves the wheel axis to aposition 60',

In addition to this turning displacement a linear displacement of thewheel with respectto the'work is re- :quired to advance the wheeloutline a distancez over point 81'. In the present case'this advance'isbest ob-: tained by a depthwise displacement z which depends onthei'inclination of the tooth normal, or the normalpre's sure angle (,0at point 81', as follows! Thus at the tooth ends, the grinding wheelshould bc relatively advanced depthwise an amount'z and it should berelatively turned on an axis 85 through an angle which produces therequired helix angle change I, and which amounts to:

Both of these displacements move the wheel further into the work so thatthe outline 77. of the wheel in the drawing plane of Fig. 9 becomeslarger.

The same is true for the opposite side of the teeth which is referred toin Fig. 10. The points 81 82 82,,, and the line 85 in Fig. 10 correspondto the points 81, 82, 82 and the line 85, respectively in Fig. 9, butrelate to the opposite side of the tooth space. The described conditionsapply also when both sides of the tooth space are ground simultaneously.This desired case is illustrated in Fig. 11 where the grinding wheel isalso shown near one of the two end positions.

The distance b of the projected wheel axis 60 from turning axis 85 inFigs. 8 to 10 amounts to the product of the wheel radius R to point 81'and turning angle t It is:

i in radians This is further shown in Fig. 12 which is a View along theaxis of the grinding wheel. Dotted line W shows the grinding wheelperiphery in a position to grind teeth without ease-off. Full lineposition W shows the actual grinding position. The wheel is fed indepthwise a distance z so that the wheel axis is displaced from position60 .to position 60 Simultaneously it is turned on axis 85 through theabove defined angle t whereby the wheel axis is displaced from position60 to 60'. It has then a distance b from the plane 6085. Its depthwisedistance z from the initial position 60 is made up of a distance z andof the depthwise elevation of position 60 over position 60'. The latteris:

/zt R After transformation the total amounts to:

e ztzzd l+ R tan 50) These two displacements b and z can be obtained inaccordance with my invention by moving the grinding wheel axis 60 aboutan axis 87 (Fig. 12) parallel to axis 60. Radius r ='6087 and theturning angle 0 about axis 87 has to fulfill the equations:

Zt= /20 r b=t9r By'division and 22 b Hence, also,

This determines pivot, 87 and the point of swing 0 about it.

The swing is in one direction at one end of the tooth space and in theopposite direction at the other tooth end. As the wheel goes through agrinding path from one tooth space end to the other, the swinging motionabout axis 87 is continuously in one direction. The swinging positionmoves from an angle (-0) to zero and to (+0). It is proportional to thestroke. Some overtravel should be had.

The above described procedure produces the desired bearing without biasproviding the grinding Wheel and the work are very rigidly mounted.

Bearing changes can be made by altering the data z}; or b, anddetermining r and 6 over again. A reduction in b tends to slant thetooth bearing toward the direction of the line of contact 45" (Fig. 5 Anincrease in b tends to slant it in the opposite direction.

There may be an occasional demand for an ease-01f which starts onlyadjacent the tooth ends, and which leaves the middle portion of thehelical teeth entirely unaltered and Without ease-off. The curve 80(Fig. 8)- would then be composed of a straight middle portion coincidingwith the tangent 79 and of curved end portions. This kind of ease-offcan also be attained in accordance with the present invention. In thiscase the swinging motionof the wheel on axis 87 (Fig. 12) is notproportional to the stroke distance. Instead it stops at the middle ofthe stroke. The swinging motion is interrupted by a dwell at the middleportion.

Fig. 13 shows diagrammatically the gist of the method of obtaining acontrolled tooth ease-01f in accordance with the present invention. Itcomprises feeding the wheel in relative to the work substantially inproportion to the square of the distance s from the mean point, and inalso changing the grinding wheel position so that grinding contact withthe lengthwise tooth curves 80 can be effected immediately adjacent aline parallel to the gear axis 36. The two end points of the curve 80are then ground in positions displaced from one another in the directionof the gear axis. While this is true for the grinding points themselves,the corresponding point of the wheel axis moves differently. This pointwill be referred to as the wheel center. It will be defined as theintersection with the wheel axis of a plane perpendic ular thereto andcontaining the mean point of the grinding profile, the point whichproduces the mean point of the gear tooth profile.

This definition applies to grinding wheels for grinding one side of theteeth. On wheels for grinding both sides of the teeth the wheel centeris the average of the two individual centers as above defined. The wheelcenter 89 in Fig. 4 then lies in the plane 90 of symmetry of the wheel,and is its intersection with the wheel axis 60.

In the diagram Fig. 13 the grinding wheel is defined by its plane ofsymmetry 90, by its axis 60, and by its wheel center 89. 91 denotes themiddle of the grinding area on the gear 35 defined by its outline andits axis 36. T he projected distance 89-91 equals the distance b intheend positions above referred to.

As the middle of the grinding contact area moves from 91,, to 91 and to91 in the axial direction of the work, the wheel center moves from 89,,to 89 and to 89 along a line 92 inclined to the direction of the gearaxis 36. In the preferred embodiment the swinging motion of the grindingwheel on axis 87 is continuous during a grinding pass.

In accordance with the present invention the wheel center moves relativeto the work in a direction inclined to the direction of the work axis,while describing a curve concave toward the work, and while the workturns on its axis. The direction 89 89 lies between the direction of thework axis and the direction of the teeth. The

latter coincides with the direction of the plane 90 of sym- Structurefor attaining controlled ease-ofi Figs. 14 and 15 illustrate oneembodiment of a wheelsupporting and wheel-actuating mechanism forcarrying out the method just described.

vided in the wheel head 133. While the bearings'showns.

wheel W' is h eresiecured to a shaft" 95 in conventional manner." Thisshaft; is iotatably mounted in a holder 96 which is radially adjustablein a pivot member 97. This member is adapted to swing in time with theworking stroke by means such as shown in the Part 122, which has therectangular opening, is -made--' V embodiment of Fig. 16. It is splitlengthwise into two up of two component parts 122', 122" (Fig. 16)rigidlyhaIves 97', 97" which are bolted together by bolts 98.. securedtogether by means not shown. .v Part 122' con It is'pivotally mounted ina wheel head 99 in two spaced tains a cylindrical outside surface 134which during the bearings 100, 100 which may be anti-friction bearingsgrindingpasses is engaged by a stop135 (Fig.16) Inif desired. thisposition the cylindrical surface 134 is coaxial with- Holder radiallyadjustable in pivot member 97, spaced screws 101 being provided for thispurpose. These screws thread into nuts formed integral with the bevelare plain bearings they may also be made anti-friction bearings ifdesired. The wheel head 133 is adjustable angularly for helix angleabout axis 111.

theaxis130 of the pivot member 118. Rocking motion on the pivot axis 130then leaves the position of the cylindrical surface unaffected. Itdoesnot move in, nor

gears 102. These gears are journaled in the pivot member 97, and areturned simultaneously by pinions 103 which are rigid with a common shaft104. The two end screws lfll are rigid with slidable holder 96. Themiddle screw 101 bears against an elastic disc 105 and serves to securethe radial position of the holder resiliently so that all the screws areunder load always and do not tend to shake ereby the gears 116, 117 rollon their racks.

does it moves out through the rocking motion. Part 122 -is slidable in{a transverse cylindrical-hole- 136 provided in the pivot member 118.The hole -13-; extends in the direction of the pitch planesof the racksAs the part 122 moves to theright in hole 136 it carries-.theholder 115and the grinding wheel--with it'g- The loose, The shaft ,104 isjournaled in projections of the lower half of the pivot member. It issecured in a desired turiiing position by known means (not shown) and isaccessible from the outside through a hole 107.

grinding wheel then recedes depthwise from the work, and gets clear ofthe work. The reverse occurs before the start of a grinding pass.

The. periodic advance and withdrawal of the grinding Thehdjustment ofholder 96 is to offset the wheel axis Whfielio and f WOYkhlg P05111011,The pp n 60 from the axis 37 to secure the desired localization offected y a cam This ham is rigidwhh Shah-141 tooth bearing. The wheelhead 99 is adjustable for helix Whch is mounted in the Wheel head andWhivh angle on ways 110 about an i 111 (Fi 15), W s geared. to performone complete turn between succes- 110 are curved about this axis, sivegrinding passes. This cam engagesthe cylindrical-' Flexible dust seals112 are used to protect the inside s f e except during g g gag nt i s fof thewheel head from grit. Shaft 95 and the grinding wheel .W' mountedthereon are rotated by a V-belt acting on pulley 113.

A further embodiment of a wheel head is shown in Figs.

where there is a very slight clearance between said surfaceand the cam.The position of part 122 is then determined by stop 135 (Fig. 16).

Engagement between part 122 and stop 135 part.

16 to V 7 V j 122 and theca n 140 is maintained by a spring 142 (Fig.--.1 Here the adjustment of the holder in the pivot mem- This spring s onalever 143 rotatably yber is made use of for withdrawing the wheel fromthe. mg a roller Rohef 144 bears against cyhhdhcal work. The wheel ispreferably withdrawn from the work. hf 145 Provided P In the forwardafter each grinding stroke, and it is advanced to working. Posmoh, w theP 122 engages the'stcp 135,

position again prior to each grinding stroke. In accord- 4O face 145 15coaxial with the P i ance with the present invention this advancementand The P 122 is Prhssed against stop 135 during grind withdrawal, theclapping, is preferably made in the same The P exefts Pressure which isSubstantially direction as the adjustment of the holder for eccentricitynqrmal 9 the cyhhdrical Surface 134 and which to the pivot axis, and ismade with respect to the pivot tams large downward component TheP3115422 member 7 made suflieiently free or loose in the cylindricalbore- The Shaft 95 of the grinding Wheel is here rotatably 136 so, thatthe downward pressure is transmitted to the mounted in a holder 115which has two spaced gears 116 holder 120 rather than to the how Therebythe gear and 117 rigid with it. These gears are coaxial with shaft teethof the holder Pressed tightly into teeth of 95 Gear 117 is seen also inFig 18 The tooth profiles their racks to keep the whole unit rigidduring grinding. of the two gears are alike. The teeth may be helical,and Shaft 141 rotated by Worm Wheel 146 a they are then of opposite handon the two gears. Each of of a W Y Passe? t q the adjustment axis 111the two gears meshes with a rack rigidly secured to a pivot and which 17q sd by a dotted line 147'- member one such rack is seen in Fig 18 andThe required tuned rocking motion on pivot axis 130 denoted at V forlocalization of tooth bearing is efiected by a cam Intermediate the twogears 116, 117 the holder rotata- 150 secured to shaft 141 one This sameshaft bly carries a sliding block 120 made up of two parts 120, holdscan lts Opposite 150 engages a '(Fvig 1.6) rigidly secured togetherSliding roller 151 (Flg. 18) mounted on the pivot member 118. blockisrotatable on the holder 115 on an axis coincid- Ehgagement between 5roller 151 main; ing with the axis of shaft 95 and of grinding Wheeltamed by the spring 152 indlcated m dotted lines in Fig. It isadjustable radially in a rectangular opening 121 pro- 150 easllyaccesslble and can be changed vided in a-part 122 which during grindingis fixed relareadily tive to the pivot member 118. Adjustment is. madeby General structure turning the square end of a screw 123 which isrotatably Either a vertical or a horizontal disposition of the. held insaid opening. In this adjustment the axis 60 of work axis may be used.In Fig. 20 I have shownas an shaft 95 is rad ally offset from the. axis130 of the pivot example a vertical disposition. The work 35 is ro- Imember 118. In this radial adjustment the two gears tatably mounted on aslide 156 which is radially ad- 7 116,117 rollontheir respective racks119, and because justable along ways 157 provided onthe base 158. This7' ofthe r ample axial distance from one another they mainadjustment isto bring the work into and out of optam the holder 115 exactly parallelto its initial position erative engagement with the grinding wheel. andparallel to the axis of the pivot member. Backlash The grinding wheel Wis mounted in a holder radially 7' is avoided during the grinding passesby pressing the adjustable in a pivot member, as described, which is...gearsdepthwise into their racks as will further be dedisposedinside ofawheel head 133. It is driven from scribed. j r t a motor 160 mounted onthe wheel head 133 on the op- The pivot member 118 is mounted foroscillation on posite side of the grindingwheel. The drive is by '"a itsaxis 130 in two spaced bearings 131, 132 (Fig. 17) probelt 161 to apulley 162 secured to a counter shaft 163 also mounted in bearings rigidwith the wheel head. Another pulley 164 on shaft 163 drives the pulley113 (Fig. 15) of the wheel spindle through a belt 165. This belt isshown in this diagrammatic view as a plain belt rather than a V-beltrThe belt 165 passes over a tension pulley 166 which is movable aboutshaft 163 and is kept pressed against the belt by spring means notshown. In this way a safe drive to pulley 113 is effected from a shaftwith a fixed axis even though the pulley 113 partakes of a small rockingmotion.

The wheel head 133 is mounted on a slide 167 for adjustment about anaxis 111 in accordance with the helix angle of the work. The slide 167is vertically adjustable in the direction of the work axis along guides170. This adjustment is to locate the position of axis lllrelative tothe work. The slide 167 may also be used for reciprocation if desired.

Preferably grinding is effected during the stroke in one direction onlyand the work is indexed between successive grinding strokes. Whether thelinear stroke along the work axis is performed by the Wheel or the workis a matter of choice. On large gears the wheel is preferablyreciprocated axially of the work.

One simple way of grinding helical teeth is by rotating the work at auniform rate during the whole of the grinding process. The work turnsthrough a integral number of teeth between successive grinding passes.To avoid complications this integral number is preferably kept prime tothe number of teeth of the work.

Fig. 21 shows a drive diagram of the feed motions. Motor 172 impartsrotation to a sleeve 173 through change gears 174. The sleeve 173 drivesa shaft 175 mounted on the slide 156 shown in Fig. 20. Shaft 175 drivesworm 176 through change gears 177. The worm 176 meshes with a worm wheel180 coaxial with the work.

If the linear strokes are imparted to the grinding wheel then the dottedrectangle 181 represents a known stroke mechanism which is driven fromthe sleeve 173 through gears 182. The gears 182 further operate throughother gears 183, 184 to impart motion to a shaft 185 mounted in thewheel head. Shaft 185 imparts motion to the cam shaft 141 (Fig. 17)through a worm 186 and wheel 146 to turn it at a rate of one turnbetween successive passes. Shaft 141 thus turns around completely asmany times as there are strokes. Thus the pivotal support for the wheelis oscillated once per stroke of the wheel through cam 150; and thewheel is moved into engagement with the work prior to a grinding strokeand withdrawn from engagement with the wheel at the end of each grindingstroke by operation of cam 140.

Dotted rectangle 190 represents a known indexing mechanism. With such amechanism it is possible to grind straight teeth on a given grindingmachine and thus extend its range. An indexing mechanism also has use onhelical teeth in modified procedures. If the stroke is to be performedby the work then the rectangle 190 also represents a known strokemechanism in addition to an index mechanism. Of course, there is onlyone stroke mechanism. If the work is reciprocated there is no need forreciprocating the grinding wheel. My described method and means forapplying controlled tooth ease-oif can be used with any one ofheretofore known methods of grinding helical gear teeth with a grindingwheel of curved, or even straight, axial profile. The ease-01f may beapplied to either one or both members of a gear pair.

The wheel dressing and truing device The wheel dresser has not beenshown onthe diagrammatic drawings of Figs. 20 and 21. A; preferred formof wheel dressing and truing mechanism -'will now be described.Its'principles are illustrated in Figs. 22 and 23.

The end diamond 200 merely serves to dress off the periphery of thewheel W. If the tooth space bottomis left unground a straight dressingpass is suflicient. Otherwise the corners of the wheel profile should berounded off in known manner.

The sidedressing diamonds 201, 202 have to dress the curved sideprofiles 204, 205 of the wheel. These profiles usually have varyingcurvature, being more curved adjacent the point of the wheel thanfurther back. This is illustrated by the circle 206 which is the circleof curvature at the mean point 207 of the active grinding profile. Theprofile 204 hugs the curvature circle 206 very closely adjacent point207, then extends outside of it further back on the wheel, while moretoward the point of the wheel it tends to reach inside of the curvaturecircle. Non-circular curve 204 has an evolute 208 (Fig. 22) and isgenerally similar to an involute. 209 denotes the surface normal atpoint 207. The tangent plane at point 207 to the wheel surface isperpendicular to the surface normal.

In accordance with my invention the diamond point, which in one positioncoincides with the point 207, is turned about a dresser axis 210 (Fig.23) inclined at an acute angle to the wheel surface and to said tangentplane and passing through the mean normal 209. The axis 210 lies in thedrawing plane of Fig. 23 and is so positioned that at point 207 thediamond moves in the direction of the axial wheel profile. point 207lies in an axial plane of the wheel.

As the diamond turns on dresser axis 210 it describes a circle aboutsaid axis. This circle shows up as a straight line 211 in Fig. 23. Shownwith exaggeration the diamond moves from a position 207 to a position212.

As the described circle does not lie exactly on the desired surface ofthe grinding wheel, the dresser is advanced along its axis 210 tocompensate for the difference. The diamond thereby moves from a position212 to a position 213 (Fig. 23) which corresponds to a point 213' of thegrinding wheel profile (Fig. 22). When the diamond motion is tangent toan axial plane at point 207, as described, the dresser axis 210intersects the surface normal 209 at the curvature center of the axialprofile that would be produced on the grinding wheel without motionalong the dresser axis. This can be demonstrated mathematically.

In accordance with my invention the dresser is so adjusted that its axis210 intersects the surface normal 209 in the center of curvature 215 ofthe required grinding wheel profile. Without any axial advance of thedresser the diamond would then produce a substantially circular wheelprofile which has the same curvature radius 207- 215 as the wheelprofile requires. Then the axial motion of the dresser has to make uponly for the slight difference between the profiles of the same meancurvature radius.

To attain a curvature center 21 5, the dresser axis 210 is set to passthrough this center. Should a curvature center 215' be required, thenthe dresser axis is set to the dotted position 210' where it passesthrough point 215'.

The axial motion of the diamond is controlled by means of a cam andfollower, one of which is held stationary,

. and the other of which is rigid with the diamond carrier.

In the embodiment specifically illustrated the cam is the stationarymember. It is a face type cam. As the swing of the diamond carrier islimited, only a fraction of the entire circumference of the cam is sweptby the follower. It is therefore feasible to put several cam profiles onthe same cam member.

Fig. 27 is a partial development of the cam. Follower 220 contacts thecam profile 221 at a point 222 which corresponds to the position of thediamond at the mean point 207 of the active grinding profile. As thedresser is set to dress the required profile curvature at point 207 evenwithout axial motion, the cam 221 has to provide very little axialmotion in that region. 222 is a point of inflection on the cam profile.When the follower 220,

The direction of the motion at l l o.

turns from right to left in engagement with the cam profile it movesup-or forward axially until it reaches the proximity of point 222. Thereits axial motion stops briefly, and then gradually continues in the sameforward direction. More broadly its minimum axial motion is at the meanpoint 222,'and it moves in the same direction axially on both sides ofthis point, as it swings over the cam profile from one end of swing tothe other end;

The above characteristic of the cam profile can be expressedinmathematical terms using the profile tangent at point 222 as one axis ofa coordinate system, and the verticaldirection as the other axis, point222 being the origin. -The ordinate y is then the distance of a givenprofile point from the profile tangent at the point of inflection 222.And the lateral distance of the profile from origin 222 is the abscissax. It is measured in the direction of-the profile tangent at the origin222.

The cam profile can then be expressed by the following equation: y=Cxwhere C is constant. 1 This omits possible higher orders, that is,terrnswhere x appears at a higher power than the cube.

In accordance with the present invention, the profile curvature isautomatically changed very gradually as the wheel diameter changesthrough repeated dressing and truing. As pointed out, a concave'wheelprofile should become more curved as the wheel diameter is reduced toproduce a constant profile on the helical teeth. This is done by tyingup the turning position of the cam 221v with-the diameter of thegrinding wheel, that is, with the position of the dresser slide which isadjustable radially toward the grinding wheel.

It will now be shown that small changes of the turning position of thecam result in small changes of the curvature radii produced on the wheelprofile. sumed that the cam is so set that a point of the cam profilewith abscissa dx contacts with the follower 220 while the diamond is atthe mean point 207 as before. The-abscissas correspond to turning anglesfrom the new mean position on the cam. Theynow amount to:

ligible as compared with the terms in dx. Thus we obtain:

at the small amountsof dx considered. 1

As will be recognized, the term in 1: results in'a change Let it be asincurvature .of the path described by the diamond, and of the curvatureproduced on the wheel profile. It is seen then that a small change inthe cam timing effects primarily a curvature change on the wheelprofile.

Structure of the dressing mechanism Referring particularly to Fig. .24,diamond 201 is provided in a pivoted part 251. For adjustment, a tool 1may be used which engages a threaded hole 232 provided. in. the holder.The holder is secured in any adjusted position by a screw 233 with asquare end. This screw. threads into. the threaded holeprovided in thepivotedpart 231and acts on the holder through a cylindrical pin 234 withan inclined plane end 235. This end contacts -the=adjacent plane side.236 (Fig. 25) of the holder. An elastic disc"237iis interposed betweenthe screw 233 and pin 234 to maintain pressure at all times and tothereby secure screw 233 against accidental rotation.

Part 231'has a pivot axis 210 inclined at an acute angle to the holder226' and tothe line of'adjustment 230.

Axis 210-intersects the line. 230. The pivoted part 231 is mountedforoscillation about and motion along its axis 210 in a housing 240, beingjournaled on two spaced bearings 241, 242'. Thefront bearing 241 extendsaround the holder 226. Thisbearing is cut oif in front at an angleso-thatthe' bearing portion around its periphery has varyingaxialpositions. The upper portion 241 is farther advanced axially. Theother bearing 242 is a more conventional bearing' It is disposed at therear. By using a front bearing 241 which extends partly beyond holder226 a sufiicient spread of the two bearingsis obtained'lfor mounting thepivoted part 231 rigidly in a confined space. i v

A sleeve 245 is threaded onto a stem 246 of the pivoted part 231 andfits about the cylindrical portion 247 of this stem... Sleeve245-contains a cam follower 220, and its cylindrical-outside surface 250serves as a bearing surface in bearing 242. A coil spring 251 isinserted between a shoulder 240 ofhousing 240 and an opposed shoulder onthe outside surface of sleeve 245. This spring presses the follower220-against the cam 252 whose cam profile has already been described.

After partial assembly, the sleeve 245 is secured again turning motionon the stem 246, for instance, by a pin extending through coaxial holes-253 of the stem and sleeve, or in any other suitable known way.

' Pivoted part 231 contains helical teeth 254. They engage rack teethrigid with a hydraulic piston not shown in Fig. 24 so that thepivotedpart may be oscillated by such conventional hydraulically actuatedmeans.

Face cam 252 contains teeth 255 on its outside, which are engaged-bymatching teeth provided internally in a ringmember 256. These teethserve for coupling, that is, rigidly connecting the cam and ring member256.

The ring member is maintained stationary in the grinding operation; butit is turned when the dresser slide (not shown in Fig. 24) is advancedtoward the wheel axis. To this end it is mounted on the housing 240 bymeans of a ball bearing257 with double contact. The ring member furthercontains the worm.- wheel teeth 260 for engagement with a worm not shownin Fig. 24. An end plate .261 is rigidly secured to the ring member 256and holds the cam member axially.

The dresser or truing apparatus obviously will be protected from .dustbyconventional dust seals. I have shown, however, a seal-262 at the frontbecause of its more unusual-construction. It is a flexible seal made forinstance of synthetic rubber bonded to the conical front end 263 of part226. At its other end it is secured ingrooves 264 provided on housing240 by a clasp 265 of known construction.

Even without the provision for changing the cam timing, this dresser hasmerit. It is simple and it maintains the diamond at a nearly constantangle to the grinding wheel-surface. This makes it possible to usediamonds other than those lapped to a single sharp point.

The'dressenshown in Fig. 26 has no adjustment for changing the camtiming. Here the cam is formed on the hub 270 of a flanged member 271which is bolted directly to the housing 240. I have shown here a squareprojection 272 on the stem'246 of pivoted part 231. It permits handoperation with a suitable tool should such hand operation be .desired.The preferred operation is howeverby hydraulic means as in'the dresserof Fig. 24.

One way of arranging a pair of dressers is indicated in Fig. 28. Thedressers are of the type described but are more diagrammatically shownthan in Figs. 24 and 26.

Each holder 226 is adjustable toward and away from the grinding wheel ina pivoted part 231, preferably along the mean surface normal 275. Thepivoted part contains a cam follower 220 engaging a face cam 252.

The pivoted part 231 is mounted in a housing 240 formed integral with orrigid with a slide 276. This slide is here mounted on a circular slide277 for adjustment in the same direction 275 as the holder 226. Thecircular slide can be adjusted angularly for pressure angle about a pin280 whose axis is perpendicular to line 275 and intersects the pivotaxis 210 at an acute angle. The circular slides 277 of the two oppositedressers are adjustable about their pins 280 on a common slide 281, towhich these pins are secured. This common slide is adjustable in astraight line to move the pair of dressers radially toward or from theaxis of the grinding wheel.

In this illustrated embodiment a ball linkage effects a change in thecam timing as the wheel diameter is reduced. The stationary ball joints282 are located on a slide 283 adjustable in the same direction as theslide 281 but held stationary after initial adjustment. These joints areindicated by their external spherical portions only. Each cam containsanother ball joint 284 at a given distance from its axis. The connectinglink is indicated by the straight line 285. It is adjustable for length.

To effect an angular adjustment of each cam 252 upon adjustment of theircommon slide 281, the two joints of each link have to be at differentvertical levels with respect to the drawing plane. If they were at thesame level a moderate adjustment of the slide 281 would leave the camtiming practically as it was. The larger the inclination of the linkaxis to the drawing plane, however, the more adjustment of the cams willresult at a given displacement of the common slide 281. The saidinclination at the middle position of the common slide 281 can be set tothe desired amount by adjusting slide 283, and then looking it.

Instead of the shown linkage I may also use the cam timing controldescribed below.

The dressing and truing device illustrated in Figs. 29 and 30 differsfrom the dresser of Fig. 28 in that the pivoted parts 231 are set at afixed inclination on a common slide 286 which is adjustable to move thedressers toward or from the wheel The housing 240 is shown here merelyby slide 287 with which it is rigid. The two opposite slides 287 areadustable at right angles to the adjustment of the common slide 286,that is, in a direction parallel to the wheel axis. They are soadjustable directly on the common slide 286.

Fig. 29 shows diagrammatically one way in which the device may beoperated hydraulically. The hydraulic cylinders 288 are rigidly securedto the common slide 286. A pair of pistons 289 formed in one piece areadapted to reciprocate therein. They act on a bar 290 through a joint291. This bar is pivoted at its opposite end in a ring 292, whichengages a sleeve 293. The latter contains internal threads. The threadon one side is a right hand thread. On the other side it is a left handthread. The internal threads are engaged by the threaded ends of theracks 294 which engage helical teeth 254 (Fig. 24) provided on thepivoted parts 231. When the pivoted parts are locked, turning of sleeve293 will move the opposite slides 287 equally in opposite directions atthe same time.

Intermediate the ring 292 and joint 291 the bar 290 passes throughanother joint 295 which is similar to joint 291. This joint 295 isstationary and adjustable along the guides 296 in the general directionof bar 290. It serves as a fixed pivot for the bar but permitslengthwise movement of the bar.

Each of joints 291 and 295 comprises a cylindrical pivot 297 which isslotted to receive the bar 290. The outside surface of this pivot isrotatable in the cylindrical inside surface of abearing portion (thebearing portions 18 of pistons 289 in the case of joint 291, forinstance), which is recessed at both ends to clear said bar.

In the described construction the amount of swing of both pivoted parts231 is simultaneously adjustable. To shorten the swing, joint 295 isadjusted toward ring 29 2. To lengthen the swing, said joint is adjustedaway from ring 292. The position of the swing is also adjustable. Afterlocking the slides 287 in their desired positions and leaving thepivoted parts free to turn, a turning adjustment of the sleeve 293 inone direction swings both pivot parts down. In this way the meanposition of swing may be altered as desired.

The end diamond 200 (Fig. 22) may be made to move with ring 292 ifdesired.

As indicated in Fig. 24, the cam 252 is adjusted by means of the teeth260 provided on a worm wheel rigid with the cam. Each Wonn wheel 260meshes with a worm 298 (Fig. 30).

The worms 298 are rotatably mounted on the respective slides 287 andtheir shafts have splined connection with a worm wheel 299 having a longhub 300. A worm 301 meshes with the worm wheel 299. It is driven fromthe spindle 302 by means of change gears 303 indicated by their pitchcircles only. This spindle is mounted on common slide 286 in an axiallyfixed position. It contains a screw (not shown) for adjusting slide 286through engagement of said screw with a stationary nut.

As the common slide 286 is adjusted by turning spindle 302, the worms298 are also turned in time therewith. They turn worm wheels 260, andthereby the cams 252 so that the dressed wheel profile becomes morecurved as the wheel diameter is reduced in the amount required forgrinding helical teeth.

The two worms 298 like the two cams 252 are of opposite hand to obtainthe desired result simultaneously on both side dressers by rotating bothworms in the same direction. I

The described method of automatically changing the wheel profile withthe wheel diameter permits of obtaining a constant product with apractical range of wheel diameters before a new set-up is required. Iteliminates a defect of the conventional process.

While the invention has been described particularly with reference togrinding, it is understood, as previously stated, that the invention isapplicable also to cutting of gears. The term gear as used herein isintended to include all forms of helically toothed members includingworms.

Having thus described my invention, what I claim is:

l. The method of producing helical side tooth surfaces on a gear whichcomprises engaging a disc type rotary tool with a gear blank, androtating the tool in engagement with the blank, while effecting arelative helical motion between the tool and blank about and in thedirection of the blank axis, and while simultaneously effecting afurther relative motion between the tool and blank in a plane which isperpendicular to the tool axis and which is inclined to the blank axisand in which the tool center travels in a path which is concave towardthe blank.

2. The method of producing helical side tooth surfaces on a gear whichcomprises engaging a disc type rotary tool, that has opposite sideworking surfaces that are of curved profile in axial section and thatare symmetrical to a central plane perpendicular to the tool axis, witha gear blank so that said plane is inclined to the axis of said blank,and rotating the tool in engagement with the blank while eifecting arelative helical motion between the tool and blank about and in thedirection of the blank axis to elfect working passes of the toollongitudinally of the workpiece, and while simultaneously effecting afurther relative motion between the tool and blank in said inclinedplane which is continuous in one direction and without reversal duringeach working pass.

3. The method of producing helical side tooth surfaces on a gear whichcomprises engaging a disc type rotary tool, that has oppositesideWorking portions that lie, respectively, on opposite sidesof. a meanplane perpendicularto the tool'axis and that lie, respectively, inseparate surfaces of;revolution coaxial with. the tool, with oppositeside tooth surfaces of a gear blank so that said plane, is inclinedtothe axis of said blank, and rotating the tool in engagement with theblank while, effecting a relative helical motion between the tool andblank about and in the direction of the blank axis, and whilesimultaneously effecting a further relative motion between the tool andblank in a direction approximately lengthwise of the engaged side toothsurfaces and about an axis which is ofiset from but parallel to the toolaxis and which is offset from the tool axis in a direction approximatelyradial of the blank.

4. The method of producing helical surfaces on a workpiece whichcomprises engaging a rotary tool, that has working portions disposed ina'surface of revolution extending about the tool axis, withthelworkpiece,.so that a plane, which is perpendicular to the'tool axis,is inclined to the axis of the workpiece, and rotating the tool inengagement with said workpiece while effecting a relative helical motionbetween the tool and rworkpiece about and in the direction of the axisof the workpiece, and while simultaneously effecting a further relativemotion between the tool and workpiece inthedirection of a mean helix ofthe engaged helical tooth surfaceto be produced on the workpiece and,about an axis. perpendicular tosaid main helix, the tool axis beingoffset from the last-named axis in a direction approximately radial ofthe workpiece.

5. The method of producing helical side tooth surfaces on a gear whichcomprises engaging a disc type rotary tool, which has opposite sideworking surfaces that are symmetrical with respect to a mean planeperpendicular to the tool axis, with a gear blank so that said plane isinclined to the axis of the blank, and rotating. the tool on its axis inengagement with the blankjwhile eliecting a relative helical motionbetween the tool and blank about and in the direction of the blank axis,and while simultaneously effecting a further relative motion between thetool and blank in a plane, which is inclined to the blank axis, in timewith said helical motion and in which the tool center travels in a pathwhich is concave toward the blank.

6. The method of producing helical side tooth surfaces on a gear whichcomprises engaging a disc type rotary tool which has opposite sideworking surfaces that are disposed at opposite sides of a mean planeperpendicular to the tool axis and that are of curved profile in anaxial plane, with a gear blank so that said plane is inclined to theblank axis, and rotating the tool in engagement with the blank whileeifecting a relative helical motion between the tool and blank about andthe direction of the blank axis, and while simultaneously effecting afurther relative motion between the tool and blank about an axis, whichis perpendicular to the general direction of the engaged tooth surfaces,in time with said helical motion and in which the tool center moves inan arcuate path concave to the blank.

7. The method of producing helical surfaces on a workpiece whichcomprises engaging arotary tool, that has working portions disposed in asurface of revolution extending about the tool axis, with the workpiece,so that a plane, which is perpendicular to the tool axis, is inclined tothe axis of the workpiece,-'and rotating the tool in engagement withsaid workpiece while effecting a relative helical motion between thetool and workpiece about and in the direction of the axis of theworkpiece, and while simultaneously effecting a further relative motionbetween the tool and workpiece about an axis parallel to the tool axisand offset therefrom in a direction approximately radial of theworkpiece, in time with and substantially in direct proportion to, saidhelical motion L 8; The method of producing helical side tooth surfaceson a gear which comprises engaging a disc type rotary tool, which hasopposite side working surfaces of curved axial profile symmetrical withreference to a mean plane perpendicular to the tool axis, with a gearblank with the tool inclined to'the blank axis at an angle larger thanthe helix angle at the pitch radius of the blank, and rotating the toolin engagement with the blank, while simultaneously effecting a relativehelical motion between the tool and blank about and in the direction ofthe blank axis.

9. The method of producing helical side tooth surfaces on a gear whichcomprises engaging a disc type rotary tool, which has opposite sideworking surfaces of curved axial profile symmetrical with reference to amean plane perpendicular to the tool axis, with a gear blank with thetool inclined to the blankaxis at an angle larger than the helix angleat the pitch radius of the blank, and rotating the tool in engagementwith the blank, while simultaneously effecting a relative helical motionbetween the tool and blank about and in the direction of the blank axis,and while simultaneously effecting a further relative motion between thetool and blank about an axis which is perpendicular to the generaldirection of the engaged tooth surfaces in time with said helical motionand which is offset from the tool axis in a direction approximatelyradial of the blank.

10. The method of producing helical side tooth sur faces of convexprofile shape on a gear which comprises engaging a disc type rotarytool, which has opposite side working surfaces that are of concavecurved axial pro file but less curved than the profiles of the toothsurfaces which are to be produced, with a gear blank with the toolinclined to the blank axis at an angle large than the helix angle at thepitch radius of the blank, and rotating the tool in engagement with theblank, while simultaneously efiecting a relative helical motion betweenthe tool and blank about and in the direction of the blank axis, andwhile simultaneously effecting a further relative motion between thetool and blank about an axis parallel to but offset from the tool axisand in time with said helical motion.

11. In a machine for grinding helical gear teeth, a rotatable toolsupport, a rotary disc-shaped grinding wheel having a curved axialprofile secured to said tool support to rotate coaxially'therewith, arotary work support, a pivoted carrier on which said'tool support ismounted, said carrier being oscillatable about an axis parallel to theaxis of said tool support and displaced from the axis of said toolsupport in a direction approximately radial of the axis of said worksupport, means for adjusting said tool support on said carrier to offsetthe axis of said grinding wheel from the axis of said carrier in saiddirection, means for turning said carrier on its axis in time withrotation of said work support, and means for effecting a furtherrelative motion between the tool support and work support in thedirection of the axis of the work support and in time with the rotationof the work support.

12. In a machine for grinding helical gear teeth, a rotatable toolsupport, a rotary disc-shaped grinding wheel, having a curved axialprofile, secured to said tool support coaxially thereof to rotatetherewith, a rotary work support, means for effecting a,relative helicalmotion between the tool and work support, about and in the direction ofthe axis of the work support in repetitive strokes, a pivoted carrier onwhich said tool support is mounted, said carrier being oscillatableabout an axis parallel to the axisof said tool support, means for ad-'justin'g said tool support in said carrier to offset the axis of thegrinding wheel mm the axis of said carrier in adirection approximatelyradial of said work support, means for rotating said tool support, andmeans for oscillating said carrier on its axis in time with said strokesso that one complete oscillation corresponds to one complete stroke andthecnds of said oscillation oc- 21 our at about equal distances from themiddle of said stroke.

13. In a machine for grinding helical gear teeth, a rotatable toolsupport, a rotary disc-shaped grinding wheel, having a curved axialprofile, secured to said tool support coaxially thereof to rotatetherewith, a rotary work support, means for effecting a relative helicalmo!- tion between the tool and work supports about and in the directionof the axis of the work support in repetitive strokes, a pivoted carrieron which said tool support is mounted, said carrier being oscillatableabout an axis parallel to the axis of said tool support, means foradjusting said tool support in said carrier to offset the axis of saidgrinding wheel from the axis of said carrier, means for rotating saidtool support, means for oscillating said carrier in time with saidstrokes so that a complete oscillation of said carrier occurs for eachsaid stroke and the ends of said oscillation occur at about equaldistances from the middle of said stroke, and means for withdrawing saidgrinding wheel from working position at the end of each said stroke andfor advancing the grinding wheel into working position again prior toeach working stroke.

14. In a machine for grinding helical teeth, a rotatable tool support, arotary disc-shaped grinding wheel, having a curved axial profile,secured to said tool support coaxially thereof to rotate therewith, arotary work support, means for eflecting a relative helical motionbetween the tool and work supports about and in the direction of theaxis of the work support in repetitive strokes, a pivoted carrier onwhich said tool support is mounted, said carrier being oscillatableabout an axis parallel to the axis of said tool support, means foradjusting said tool support in said carrier to offset the axis of saidgrinding wheel from the axis of said carrier, a head in which saidcarrier is mounted, means for rotating said tool support, a shaftjournaled in said head, means for rotating said shaft once for eachstroke cycle, and means actuated by said shaft for moving said toolsupport in opposite directions at opposite ends, respectively, of saidstrokes to move the grinding wheel, respectively, into and out ofoperative position, and means actuated by said shaft for oscillatingsaid carrier in time and approximately in proportion with said strokesso that a complete oscillation of said carrier occurs for each stroke.

15. In a machine for grinding helical teeth, a rotatable tool support, arotary disc-shaped grinding wheel secured to said tool support coaxiallythereof to rotate therewith, a rotary work support, means for effectinga relative helical motion between the tool and work supports about andin the direction of the axis of the work support in repetitive strokes,a head adjustable about an axis perpendicular to the axis of the toolsupport, a carrier mounted in said head for oscillation about an axisparallel to the axis of said tool support, means for adjustablysupporting said tool support on said carrier for adjustment thereon tooffset the axis of the tool support from the axis of said carrier, meansfor rotating said tool support, a shaft journaled in said head, meansfor driving said shaft at the rate of one full turn for each strokecycle, a cam secured to said shaft and operatively connected to saidcarrier to oscillate said carrier, and a second cam secured to saidshaft and operatively connected to said carrier to move said grindingwheel into and out of grinding position in time with said strokes.

16. A machine for producing helica'l side tooth surfaces on a workpiece,comprisinga rotary tool support, a rotary disc-shaped tool secured tosaid tool support coaxially thereof to rotate therewith, a rotary worksupport, means for adjusting the tool support angularly to incline amean plane perpendicular to the axis of the tool to the axis of the worksupport, means for rotating the tool support, means for rotating thework support, means for effecting a relative feed movement between thetool support and the work support in the direction 22 of the axis of thework support and in time with the ro-" tation, of the work support, andmeans for effecting a continuous relative movement without reversalbetween the tool and work supports, in said mean plane in time with saidfeed movement.

17. A machine for producing helical side. tooth sur= faces on aworkpiece, comprising a rotary tool support, a rotary disc-shaped toolsecured to said tool support coaxially thereof to rotate therewith, arotary work sup port, means for adjusting the tool support angularly toincline a mean plane perpendicular to the axis of the tool to the axisof the work support, means for rotating the tool support, means forrotating the work support, means for effecting a relative feed movementbetween the tool support and the work support in the direction of theaxis of the work support and in time with the rotation of the worksupport, and means for effecting relative movement between the tool andwork supports in said mean plane in time with said feed movement andapproximately longitudinally of the engaged tooth sides, and in whichthe center of the tool travels in a path concave toward the work.

18. A machine for producing helical side tooth surfaces on a workpiece,comprising a rotary tool support, a rotary disc-shaped tool secured tosaid support coaxially thereof to rotate therewith, a rotary worksupport, means for adjusting the tool support angularly relative to thework support to incline a plane perpendicular to the tool axis to theaxis of the work support, means for rotating the tool support, means forrotating the work support, means for effecting a relative. feed movementbetween the tool support and the work support in the direction of theaxis 'of the work support and in time with the rotation of the worksupport, and means for effecting relative movement between the tool andwork supports in time with said feed movement and approximately inproportion to said feed movement and about an axis parallelto but offsetfrom the axis of said tool support in a direction approximately radialof the axis of the work support. I I

19. A machine for producing helical side tooth surfaces on a workpiece,comprising a rotary tool support, a rotary disc-shaped tool secured tosaid support coaxially thereof to rotate therewith, a rotary worksupport, means for adjusting the tool support angularly relative to thework support to incline a plane perpendicular to the tool axis to theaxis of the work support, means for rotating the tool support, means forrotating the work support, means for effecting a relative feed movementbetween the tool support and the work support in the direction of theaxis of the work support and in time with the rotation of the worksupport, means for effecting relative movement longitudinally of thehelical side tooth surfaces between the tool and work supports in timewith said feed movement and about an axis parallel to but offset fromthe axis of said tool support, and means for effecting further relativemovement between the tool and work supports in a direction perpendicularto said parallel, offset axis at opposite ends of said feed movement tomove the tool in and out of engagement with the work, respectively.

20. In a machine for producing tooth surfaces on a cylindrcal workpiece,a rotatable tool support, a rotary disc-shaped tool secured to said toolsupport to rotate coaxially therewith, a rotatable work support, apivoted carrier on which said tool support is mounted, said carrierbeing oscillatable about an axis parallel to the axis of said toolsupport, means for effecting a relative feed motion between said carrierand said work support in the direction of the axis of the work support,and means for turning said carrier on its axis in time with said feedmotion and approximately in proportion thereto.

21. The method of producing essentially helical tooth surfaces on arotatable cylindrical work piece which comprises engaging a disc-typerotary tool with a work lation whose mean direction is inclined to theaxis of the work piece, while the tool axis is 'maintained at a constantangle to the axis of the workpiece.

22. The method of producing essentially helical tooth surfaces on arotatable cylindrical work piece, which comprises engaging a disc-typerotary tool with a work piece so that the axis of said tool is angularlydisposed to the axis of the work piece, rotating said tool in engagementwith the work piece while turning the work piece on its axis and whileeffecting a relative feed motion between the tool and the work pieceacross the face of the work piece, said feed motion being a translationin a plane inclined to the axis of the workpiece, while the tool axis ismaintained in a constant angular position, the relative path describedin said plane being curved to produce a different tooth thickness at theends than at the middle of the teeth; a

23. In a machine for producing tooth surfaces on a cylindricalworkpiece, a rotatable tool support, a rotary disk-shaped toolsecured tosaid tool support to rotate coaxially therewith, a rotatable worksupport, a pivoted carrier on which said tool support is mounted, saidcarrier being oscillatable about an axis parallel to the axis of saidtool support, means for effecting relative feed motion between saidcarrier and said work support in the direction of the axis of the worksupport, and means for turning said carrier on its axis in time'withsaid feed motion to move said tool in an are extending approximately inthe longitudinal direction of the tooth surfaces engaged by said tool. 7V

24. In a machine for producing tooth surfaces on a cylindricalworkpiece, a rotatable tool support, a rotary disc-shaped tool securedto said tool support to rotate coaxially therewith, a rotatable worksupport, afpivoted carrier on which said tool supportis mounted, thepivot axis of said carrier and the axis of said tool support beingarranged in parallelism, adjustment means for changing' the distancebetweensaid two axes, means for effecting a relative feed motionbetween'said carrier and said work support in the direction of the axisof the work support, means for turning said carrier on its pivot axis intime with 'said feed motion in one direction only during the operativefeed motion in one direction, and means for changing the ratio of saidturning motion to said feed motion.

25. The method of producing tooth surfaces on a cylindrical workpiece,which comprises providing a disktype rotary tool having working portionsdisposed in a surface of revolution of concave'axial profile and ofconvex profile in peripheral direction, rotating said tool on its axisin engagement with a cylindrical workpiece, efiecting a relative feedmotion between said tool and work piece in the direction or the axis ofsaid Work piece, elfecting a distinct additional motion between saidtool and workpiece by which the tool axis is moved relative to theworkpiece in an arc in an' average direction lengthwise of the toothsides engaged by said tool while maintaining the tool axis and the axisof the workpiece each in a fixed direction, said additional motion beingin one direction only during the operative part of the feed motion inone direction, and repeating said motions on other teeth of saidworkpiece. 1

References Cited in the file of this patent UNITED STATES PATENTSGriflin Oct. 21, 1 952

